Motor and self-synchronous generator frequency synchronization units for swept frequency secret communications system



Oct. 22, 1968 x. P. WHEELER 3,407,354

MOTOR AND SELF-SYNCHRONOUS GENERATOR FREQUENCY SYNCHRONZATION UNTS FOR SWEPT FREQUENCY SECRET COMMUNICATIONS SYSTEM Filed Apr-11 9, 1942 lll.

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E k EWI I llllllllllllllllllllllllllll ll v vv c YH ox Josep/z l? Wheeler MM! www United States Patent O1 hcc 3,407,354 Patented Oct. 22, 1968 A 3,407,354 4 MOTOR AND SELF-SYNCHRONOUS GENERATOR FREQUENCY SYNCHRONIZATION UNITS FOR Y SWEPT FREQUENCY" SECRET COMMUNICA- TIONS SYSTEM Joseph P. Wheeler, Naval Research Laboratory,

Washington, D.C. 20360 'y n Filed Apr. 9, 1942, Ser. No. 438,322 1 Claim. (Cl. 325-35) This invention relates to a system by means of which two-wave radio communication may be maintainedrwith substantially no possibility of detection by anyone not equipped with apparatus constructed according to the invention. .A p

It is an object of this invention to provide such a system ina form which is simple and rugged. 1

It is'a further object of this invention` to provide a communication system which utilizes a plurality of transmitting and receiving units located ata plurality of separated stations, all of which units vary continuously in frequency Vduring their operation, the frequency variation of all units being synchronized.

It is another object of this invention to provide a communication system as set forth above in which the operation of a transmitting unit at one of the stations automatically sets into operation a receiving unit at each of the other stations and sets the frequency variations of these units into operation in synchronism with the frequency variations of said transmitting unit.

It is another object of this inventio'nto provide a methd of two-wave radio communication which is safel from detection by undesired persons.

Other objects will become apparent from a careful consideration of the following description when taken with the accompanying drawing, the single figure of which is a schematic representation of a communication system embodying the invention.

In the preferred form of the invention the system cornprises a transmitting and a receiving unit located at each of the stations between which it is desired to maintain communication. In the drawing a pair of such stations are indicated by the boxes marked station A and station B. A transmitter and a receiver 11 are shown in station A while station B is provided with transmitter 10 and receiver 11. In carrying out the invention the frequency of the transmitter and receiver of each station is caused to vary in a predetermined manner by the use of synchronized driving means simultaneously varying the tuning of the input circuit of the receiver and the tank circuit of the oscillator of the transmitter. Thus a pair of selfsynchronous motors 14 and 15 are shown in station A driving through gear boxes 16 and 17 the variable condensers 18 and 19 in the tank circuit of the transmitter and in the tuned antenna coupling circuit of the receiver, respectively. The stator windings of the motors 14 and are connected in a three-phase circuit in parallel with the stator windings of a self-Synchronous generator driven by a constant speed motor 26 having its speed vary carefully regulated. The rotor of each motor and the generator is supplied from a common source of 110 v. A C. voltage. The A C. supply is interrupted by a starting switch 21 and a relay switch 22. The relay switch is actuated by a solenoid 23 for which power is supplied by a power amplier 24 to which is fed the LF. output of -receiver 11. A reversing switch 20 is located in the threephase circuit ahead of the motors and is operated mechanically by suitable stops (not shown) cooperating with the ygearing in gear box 17, to reverse the direction of rotation of the motors 14 and 15 at desired points in the tuning range of the variable condensers. Station B is supplied with identical equipment, the various elements of which are numbered the same as the corresponding elements in station A withthe exception that the numbers are primed. The motor l.26' must runat kthe same speed asmotor26. i

.The operation of the device is as follows;

It will ybe assumed that the starting switches 21, 21A are closed, the A.C.supply lines, however, remaining open due to the relay switch- 22. lf now it is desired to open communication from station A the relay switch 22 is closed manually, thus setting into operation selsyn motors 14 and 15. These motors now drive variable. condensers 18 and 19,at a predetermined rate vof speed and thus continuously increase or. dec rease the frequency of the transmitter and. the-receiver-.The reversing switch 20 is provided so that as the condensers18 and 19 approach the limits of their variation in one direction the directional movement of the self-synchronous motors may be reversed to reverse the direction of variation of the condensers. By changing the` gear ratio in the gear boxes 16 and 17 the rate of movement of the condensers may be varied without varying the speed of the motorsjlransmitter 10 now begins to transmit at a frequency which varies in a predetermined manner. The receiver 11 haS. been constructed to operate with the same predetermined variation of frequencies by virtue of the motor 15' driving its variable condenser 19. However, the receiver not being in operation, the setting of the condenser 19 may be at any point within that range. Neverthless, as the frequency of condenser 18 continues to vary, the transmitter 10 will finally transmit the frequency at which receiver 11 is set to respond. Reception of the signal will, through the power amplifier 24,actuate relay switch 22 to close the A.C. supply circuit to motor 15 and thus commence movement of variable condenser 19'. If the reversing switch 20 is properly set the motor 15' will continue to operate to vary the condenser 19 so that the frequencies of receiver 11' track those of transmitter 10. However, if the reversing switch 20' is set in a manner to produce rotation of motor 15 in a direction opposite to that of motor 14 movement of motor 15 will quickly tune the receiver out of the signal from transmitter 10, the relay 22 will reopen and the receiver will cease to operate, until continued movement of condenser 18 brings it back again to the setting of condenser 19', with the motor 14 moving in the same direction for which motor 15 is set.

Once receiver 11 and transmitter 10 are tracking, they will continue to do so throughout the range of frequency variation of transmitter 10. Any person attempting to intercept the message would catch only very short bits of it as the frequency of the transmitter passed through the frequency being watched and detection would be impossible unless the frequency of the detecting receiver could by some means be made to track that of transmitter 10.

Once the receiver 11 is tracking transmitter 10 all four motors will be operating in synchronism. The motor 14 will be varying the setting of condenser 18' in a predetermined manner and the motor 15 will be varying the setting of condenser 19 in a manner to cause receiver 11 to constantly track transmitter 10'. While the operation of all the motors must be synchronized, it is not necessary that the pattern of frequency variation of transmitter 18' follow that of transmitter 18. Transmitters 10 and 10 may transmit on different frequencies or their frequency variations may move in opposite directions simultaneously without adverse results. It is only necessary that receiver 11 track transmitter 10 and receiver 11 track transmitter 10.

Thus two-way communication may be maintained on separate frequency bands, if desired, and on frequencies which constantly change and thus defy detection. It is necessary that'rea'ch transmitter transmit abroad enough band"frequentiesrio-aisomeltiinelag"for v'the' chanical operation of the relays 22 and 22' and allow also for the motors 15 and 15 to'come into operation'. Thus if' ythe`-'badItlfan''srr'littedwerev to narrow, by thel time the' "rceivef was 'in ope'ratlon; thevariation of the transmitter* frequc'yfwould'have"moved*the signal beyond the frequency setting of the' receiver. l 'i e As an example ofwvalues which may be employed, the motors 26 and 26"r'n`y opera'te'as 1800fr.p'.-m. and drive the variable `condenser's throughredutiongearing in gear boxes 16, 16', `17"an d"',17 'fatspeeds" around one-sixth r.p.m'.' The frequency OBthersy'stemnay vary through a 'band of vvI0() ke;` in width; for example, from'500 to 1500 kc; andthe instantaneous transmitter` bandwidth may be 20 lc. In order to obtain" additional security, it is possible to vary 'the frequency 'changingA cycle both as'v to Vtime and the "sequencef movement; However, the introduction of such ,variationsmustte-in 'accordance with a prearrangedschedule. Many means lof varying both thefspeed and sequencev of variation will suggest 'itself to those skilled Iin the art,l such' as substitution of gear trains of I various ratios, use of cams and other means of obtaining variable motion from a fixed driving means.

While the disclosure has been limited to one embodiment of the invention, many departures therefrom both in arrangement and substitution of elements within the scope of the invention as defined by the appended claims, will suggest themselves to those skilled in the art.

The invention described herein may be manufactured and used by or for the Government of the United StatesV of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A secret communication system comprising at least a pair of stations, a transmitter unit and a receiver unit in each station, means to vary the frequency of the transa predetermined cycle of variations, the cycle of variations of each of said transmitter units being identical with that of the receiver unit in the other station of said parir, said` means tov vary thefifrequencyjn each: lolfsaid stations com 'rising'- a, variable ffr'equency "deterrninativ element controlling tliefrequericyy thereof,v a: sltsyncllronous motor connected to said variable frequenry'determinativevh Velement tot. varyt.,t h e `tuning thereoffa. self-synchronous generator driving said-motor, and a motor driving said selflsyn'chronous generator; means supplying electrical energy tofsaidvlast' named motors, means normally interrupting said supply and means actuated by the reception of a signal' by said receiver'to render said inte`rrupting means ineffective?" yReferences Cited n .UNITED STATES. PATENTS.

7/1890 `Delany .t17853.1-Xu i .1,501,711 ,f7/1924.y Heising 178-,53.LX 1,540,313v 6/.1925 Chaplin 178f543-1 1,592,940 7/1926 Kendall Q 1 1 179r-1. 1,596,251A 8/ 1926 Hammond V 3251-34 v1,607,485 1,1/1926 Schmidt 3 25--35- 1,628,411 5/1927 Kranz 325-33 X `1,634,390 7/.192'7 Zworykin 32,5-,32 2,333,719 -vl1/l943 Herold. v l V2,491,540 12/1949 Wiseman-et al. a 32,5-20

, FOREIGN PATENTS 206,499 17/ 1924 Great Britain.

ROBERT L. GRIFFIN, Primary Examinr. B. V. SAFOUREK, Assistant Examiner.' 

1. A SECRET COMMUNICATION SYSTEM COPMPRISING AT LEAST A PAIR OF STATIONS, A TRANSMITTER UNIT AND A RECEIVER UNIT IN EACH STATION, MEANS TO VARY THE FREQUENCY OF THE TRANSMITTER UNIT AND THE RECEIVER UNIT OF EACH STATION THROUGH A PREDETERMINED CYCLE OF VARIATIONS, THE CYCLE OF VARIATIONS OF EACH OF SAID TRANSMITTER UNITS BEING IDENTICAL WITH THAT OF THE RECEIVER UNIT IN THE OTHER STATION OF SAID PAIR, SAID MEANS TO VARY THE FREQUENCY IN EACH OF SAID STATIONS COMPRISING A VARIABLE FREQUENCY DETERMINATIVE ELEMENT CONTROLLING THE FREQUENCY THEREOF, A SELF-SYNCHRONOUS MOTOR CONNECTED TO SAID VARIABLE FREQUENCY DETERMINATIVE ELEMENT TO VARY THE TUNING THEREOF A SELF-SYNCHRONOUS GENERATOR DRIVING SAID MOTOR, AND A MOTOR DRIVING SAID SELF-SYNCHRONOUS GENERATOR, MEANS SUPPLYING ELECTRICAL ENERGY TO SAID LAST NAMED MOTORS, MEANS NORMALLY INTERRUPTING SAID SUPPLY AND MEANS ACTUATED BY THE RECEPTION OF A SIGNAL BY SAID RECEIVER TO RENDER SAID INTERRUPTING MEANS INEFFECTIVE. 